1. Field of the Invention
The present invention relates to an image forming apparatus including a process unit and at least one power supply unit to output voltage and current required for the operation of the process unit.
2. Description of the Related Art
An image forming apparatus, for example, a color copier includes a process unit having, as an image bearing body, a photoconductive drum and an intermediate transfer belt.
The process unit includes at least one power supply unit (so-called high voltage power supply unit) to output voltage and current required for the operation of the process unit.
Besides, the process unit includes a charging unit to charge the surface of the photoconductive drum, a laser unit to expose the surface of the photoconductive drum charged by the charging unit to a laser beam and to form an electrostatic latent image on the surface of the photoconductive drum, a development unit to supply a toner to the surface of the photoconductive drum and to develop the electrostatic latent image on the surface of the photoconductive drum into a visible image, a primary transfer roller to transfer the visible image on the photoconductive drum to the intermediate transfer belt, a secondary transfer roller to transfer the visible image on the intermediate transfer belt to a paper sheet, and the like.
The power supply unit includes a constant voltage output circuit to output a transfer voltage of the primary transfer roller, and a constant current circuit to output a constant current to measure the impedance of the intermediate transfer belt before transfer by the primary transfer roller. The impedance of the intermediate transfer belt is measured based on the constant current outputted from the constant current circuit. The level of the transfer voltage outputted from the constant voltage output circuit is determined according to the measured impedance.
An output variable signal to set the level of the transfer voltage and the level of the constant current is inputted to the power supply unit. The level of the transfer voltage and the level of the constant current are set according to the voltage level of the output variable signal. Further, ON and OFF signals to set ON and OFF of the operation of the constant voltage output circuit and the constant current output circuit are inputted to the power supply unit, and a mode switching signal to cause one of the output of the constant voltage output circuit and the output of the constant current output circuit to be outputted is inputted.